Amino acid transport: Alterations due to synaptosomal depolarization

The effect of a preliminary high potassium depolarization on the synaptosomal transport of a number of compounds was tested. It was found that a preliminary depolarization increased the transport of glutamic acid, aspartic acid, glycine and choline, all of which are known or suspected neurotransmitters or neurotransmitter precursors. Depolarization had no effect on the transport of a number of other compounds including the neurotransmitter precursor, tyrosine. The increased transports of glutamate, aspartate, glycine and choline were found to be into osmotically sensitive compartments and were not due to decreases in leakiness of synaptosomes. Kinetically, the increase in choline transport was characterized by an increase in Vmax and the increases in glutamate and glycine transport were characterized by decreases in KT. Thus, selected transport systems in synaptosomal preparations can be altered by a previous depolarization.